currently difficulty is at 37. and is estimated to jump to 50. which is ~%35 increase so, if this trend continues, we are talking ~%100 increase per month
http://mining.thegenesisblock.com/that is why I decided not to buy knc Jupiter at the moment, even if it is delivered in October as promised I still would not make ROI.
if there is a flaw in this logic please point it out I really want to get Jupiter.
You're assuming that the exchange rate of BTC will stay the same. Let's say the exchange rate goes to $200 USD / BTC or even higher, those coins you mine are suddenly much more valuable and can affect your ROI, though it may take a lot longer for you to see that.
I stopped mining back in 2010/2011 because they were only worth like $2 and it was costing more in electricity than it was worth. Had I kept mining, that investment would have more than paid off. If you are in this for the long term, then the investment could still pay handsomely.
I, personally, expect the price to rise because it will take more and more computing power to generate the same coins, pushing out the small guys and leaving only big investors with the hardware to mine, plus you have the deflationary pressures as people hoard coins.